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We present a physical characterization of main-belt comet 176P/LINEAR.Observations show the object exhibiting a fan-shaped tail in late 2005, butthen becoming inactive in early 2006. Using data from 2007 when the object wasobserved to be inactive, we derive best-fit IAU phase function parameters ofH=15.10 mag and G=0.15, linear phase function parameters of m(1,1,0)=15.35 magand Beta=0.038 mag/deg, and a rotation period of P_rot=22.23 hr and aphotometric range of delta~0.7 mag. In 2005, the nucleus exhibits asignificantly smaller photometric range that is attributed to viewing geometryeffects. An analysis of these effects showed that 176P likely has an axis ratioof 1.8<b/a<2.1, an obliquity of epsilon~60 deg, and a solstice position at atrue anomaly of ~20 deg. Numerical modeling found that 176P's activity can onlybe reproduced by asymmetric dust emission, such as a cometary jet. We findplausible fits to our observations using models assuming ~10 micron dustparticles continuously emitted over 176P's active period, and a jet directionof 180 < alpha_jet < 120 deg and delta_jet ~ -60 deg. We do not find good fitsto our observations using models of impulsive dust emission, i.e., what wouldbe expected from an impact. Since for a rotating body, the time-averageddirection of a non-equatorial jet is equivalent to the direction of the nearestrotation pole, we find an equivalent orbital obliquity of 50 < epsilon < 75deg, consistent with the results of our lightcurve analysis. The results of ourlightcurve analysis and dust modeling analysis are furthermore both consistentwith the seasonal heating hypothesis used to explain the modulation of 176P'sactivity. Additional observations are highly encouraged to further characterize176P's active behavior as the object approaches perihelion on 2011 July 01.

Physical Properties of Main-Belt Comet 176P/LINEAR